The present invention generally relates to power supplying systems, and more particularly to a power supplying system for a subscriber line terminating equipment which has the function of supplying power to a terminal equipment.
Recently, a narrow band integrated services digital network (ISDN) services which provide not only the existing telephone services but also high-speed data communication services using the existing two-wire telephone line equipments have started in order to cope with the demands for high-speed communications. For this reason, at the subscriber, the two-wire telephone line is not directly connected to a telephone set as in the conventional case, but is connected to an ISDN terminal equipment via a Network Termination 1 (NT1) which is a subscriber terminating equipment. The ISDN terminal equipment includes a digital telephone set, a Group 4 facsimile machine or the like.
In the case of the conventional telephone set or the like, the basic telephone service is provided by supplying power from a telephone station 100 using the voltage that is superimposed on a two-wire telephone line 105 as shown in FIG. 1. The commercial power supply available within a subscriber (home) 110 is used for the added functions other than the telephone service.
When receiving the ISDN service, the power supplied from the telephone station 100 is insufficient because an ISDN terminal equipment 112 shown in FIG. 2 carries out a variety of functions. Hence, the ISDN terminal equipment 112 itself uses a commercial A.C. power supply 114 within the subscriber 110 as shown in FIG. 2 to receive a local power supply or, an NT1 equipment 111 receives such a local power supply as shown in FIG. 3 to distribute the power with respect to the ISDN terminal equipment 112. In these cases, the power from the commercial A.C. power supply 114 is supplied via a power supply adapter 113 which has the function of converting the commercial A.C. power supply voltage to a D.C. voltage. In FIGS. 2 and 3, phantom arrows indicate the power supplying routes.
In the case of the power supply adapter 113 shown in FIG. 3, a battery backup is provided in order to guarantee the operation of the NT1 equipment 111 even when a power failure of the commercial A.C. power supply 114 within the subscriber 110 occurs. The battery backup of the power supply adapter 113 can supply the power with respect to the NT1 equipment 111 and the ISDN terminal equipment 112 even when the power failure of the commercial A.C. power supply 114 occurs, so that the ISDN terminal equipment 112 can at least receive the minimum telephone service.
Next, a description will be given of the methods of supplying the power from the NT1 equipment 111 to the ISDN terminal equipment 112.
An interface between the NT1 equipment and the terminal equipment prescribed by the CCITT Recommendations 1.430 is also referred to as a S/T interface. The S/T interface is made up of an interface having a total of 6 wires (or a maximum of 8 wires), namely, 4 communication wires for transmitting and receiving and 2 power wires (or feeders) for supplying power to the terminal equipment. According to the above CCITT Recommendations, two methods of supplying the power from the NT1 equipment to the terminal equipment are prescribed, namely, methods called PS1 and PS2.
FIG. 4 is a circuit diagram for generally explaining the two power supplying methods PS1 and PS2. In FIG. 4, those parts which are the same as those corresponding parts in FIG. 3 are designated by the same reference numerals, and a description thereof will be omitted.
In FIG. 4, the NT1 equipment 111 generally includes a transmitter part 131, a receiver part 132, a power supplying part 133 and a power supplying part 134. On the other hand, the terminal equipment 112 generally includes a receiver part 141, a transmitter part 142, a power receiving part 143 and a power 10 receiving part 144. The NT1 equipment 111 and the terminal equipment 112 are coupled via a S/T interface 120.
Although FIG. 4 shows two power supplying parts and two power receiving parts, this differs from the actual construction. The two power supplying parts and the two power receiving parts are merely shown in this single diagram for the sake of convenience in order to describe both the two power supplying methods PS1 and PS2 using this single diagram.
The power supplying method PS1 is also referred to as a phantom power supplying method. According to this method, a 4-wire communication line is used, and a middle point of the transformer is used to supply the power from the power supplying part 133 within the NT1 equipment 111 to the power receiving part 143 within the terminal equipment 112.
On the other hand, the power supplying method PS2 is also referred to as an exclusive power supplying method. According to this method, 2 wires unrelated to the communication are used exclusively for the power supply. In other words, the power from the power supplying part 134 within the NT1 equipment 111 is supplied to the power receiving part 144 within the terminal equipment 112.
FIG. 5 is a circuit diagram for explaining the construction of a power supplying circuit within the actual NT1 equipment with respect to the terminal equipment and the construction of the power supply adapter 113 for the NT1 equipment. In FIG. 5, those parts which are the same as those corresponding parts in FIGS. 3 and 4 are designated by the same reference numerals, and a description thereof will be omitted.
In FIG. 5, the NT1 equipment 111 is provided with an excess current limiting circuit 136 and a D.C./D.C. converter 137. The D.C./D.C. converter 137 simply converts a D.C. power supply voltage of 40 V, for example, supplied from the power supply adapter 113 into a D.C. power supply voltage of 5 V, for example, for use within the NT1 equipment 111. On the other hand, the power supply adapter 113 generally includes an A.C./D.C. converter 151 and a backup battery 152. The A.C./D.C. converter 151 converts a commercial A.C. power supply voltage of 100 V, for example, into a D.C. power supply voltage of 40 V, for example.
In the actual NT1 equipment 111, the power supply parts 133 and 134 for supplying the power by the power supplying methods PS1 and PS2 do not exist independently as shown in FIG. 5. In other words, the power is supplied by the power supplying method PS1 or PS2 by passing the D.C. power supply voltage from the power supply adapter 113 as it is through the excess current limiting circuit 136. The excess current limiting circuit 136 is provided to prevent damage to the NT1 equipment 111 and the external power supply adapter 113 when the power supply is instantaneously short-circuited or the like outside the NT1 equipment 111.
The S/T interface 120 is a terminal wiring and it is possible for the short-circuiting of the power supplying route to occur for some reason. When the power supplying method PS1 is employed and such a short-circuiting occurs for 1 wire on the transmitting side and 1 wire on the receiving side, for example, it is still possible to continue the normal communication functions of the NT1 equipment 111. On the other hand, when the power supplying method PS2 is employed and a short-circuiting occurs, it is still possible to continue the normal communication functions of the NT1 equipment 111 because the excess current limiting circuit 136 operates if the terminal equipment 112 does not use the power supply.
In addition, when the terminal equipment 112 which is coupled to the NT1 equipment uses the commercial A.C. power supply instead of using the power supply via the NT1 equipment 111, it is possible to continue the communication even when the above short-circuiting occurs. But since the terminal wiring is closed within the subscriber, the network side is not concerned with the failure of the terminal wiring, and no alarm or the like is provided with respect to the failure of the terminal wiring for the interface between the network side and the terminal equipment side.
Accordingly, even when the above described short-circuiting type failure occurs at the S/T interface 120, it is not the responsibility of the network side, and in addition, the communication service received at the terminal equipment 112 (that is, the subscriber side) is not directly affected by the failure. For these reasons, there is a high possibility that the subscriber will continue to use the terminal equipment 112 in the state where the terminal wiring is short-circuited.
On the other hand, in an extreme case, when the connection is such that the terminal equipment 112 normally operates using the commercial A.C. power supply and operates using the power supply from the NT1 equipment 111 at the time of the power failure, the terminal equipment 112 will normally operate in the normal state even if the short-circuiting type failure occurs at the S/T interface 120 but will not operate if the power failure occurs because the power supplying route will be short-circuited in this latter case.
In other words, although it is impossible to remotely eliminate the short-circuiting type failure at the terminal wiring from the NT1 equipment 111, it is desirable to somehow detect such a short-circuiting type failure. If the short-circuiting type failure can be detected, it is possible to notify the subscriber of the detected short-circuiting type failure so that the short-circuiting type failure may be eliminated.